// 定义成员：
const sum = function (a, b) {
    return a + b
}
const subtract = function (a, b) {
    return a - b
}
const multiply = function (a, b) {
    return a * b
}
const divide = function (a, b) {
    return a / b
}

//简写
module.exports = {
    sum,
    subtract,
    multiply,
    divide
}